The present invention relates to a device for applying a liquid mixture of a first liquid and at least one second liquid to web-shaped printing material.
In rotary offset printing presses, a paper web is typically unrolled off a supply roll and guided through a plurality of printing units which print the web in multiple colors on both sides using the wet offset method. For drying the web and the wet printing ink, the web is guided through a hot air dryer in which water and volatile solvents of the printing ink vaporize. For setting the liquid ink, the web is subsequently guided over cooling rolls of a cooling roll stand, the cooling rolls being flushed by a cooling medium. Finally, for producing the finished printing products, the web is fed to a folding machine which may fold and cut the web in different configurations. The finished products are then oftentimes supplied to a shipping room.
In order to prevent a buildup of printing ink on guide elements for the web, a silicone oil emulsion may be applied to the dried web in known devices. At the same time, the water content of the emulsion makes desired rewetting of the web after drying possible.
A device for applying a silicone oil emulsion to a paper web is known from U.S. Pat. No. 4,637,341. The device has a buffer and mixing tank which is connected to a reservoir for silicone oil concentrate via a supply line. The buffer and mixing tank is used, among other things, for buffering the silicone oil emulsion since, prior to reaching a lowest fill level, the reservoir is exchanged for another reservoir so that, for a certain time period of the exchange, the supply of silicone oil concentrate is not possible. In addition, the buffer and mixing tank is connected to a water source so that the tank may be used not only for buffering, but also for mixing a desired silicone oil emulsion. The mixture so produced is conveyed via a heat exchanger for heating the mixture to a trough of a respective applicator roll; the applicator roll scoops the mixture out of the trough and applies it on a paper web.
A control unit is connected to an upper sensor and a lower sensor which monitor the fill level of the buffer and mixing tank. When the fill level reaches the level of the lower sensor, the control unit opens a valve in the water supply until the fill level reaches the level of the upper sensor; then the control unit closes the valve again. Simultaneously, a desired quantity of silicone oil concentrate is delivered from the reservoir into the buffer and mixing tank so that a silicone oil emulsion having the desired mixing ratio is produced.
Several disadvantages are associated with the known device. For example, no silicone oil concentrate is buffered, but rather a silicone oil emulsion having a desired mixing ratio. This may result in the fact that the fill level of the buffer and mixing tank reaches the lowest level, replenishment of silicone oil concentrate not being immediately possible since, at the same time, the reservoir may also have reached its lowest fill level. Moreover, the buffer and mixing tank must have very large dimensions since the emulsion is used up much more rapidly than the concentrate.
Furthermore, due to the large dimension of the buffer and mixing tank, it is not possible in the known device to change the mixing ratio in the buffer and mixing tank within a short response time, in order to adjust the mixing ratio to a new print job, for example.
The known device also does not allow the application of silicone oil emulsion of differing mixing ratios on both sides of the paper web. To achieve this, the known device would have to be used separately on both sides, so that there would be a separate buffer tank for each side.
Finally, the operator is unable to predetermine the desired water-to-silicone oil ratio of the mixture, in particular separately for both sides of the web.